I can understand how she might not want to get two buses, however I would certainly offer you money to cover the toll if it was me. It's easy to get lazy if you have someone who will make all of the effort without complaint.
However, the alarm bells would be ringing to me if you can't drive to see her and she still doesn't bother to make the effort, particularly if she's going on holiday soon too. The thing I've learned with the people who I've been with in the past is that the guys I've really liked are the ones I've made the effort to see - no matter how long it takes, or how much it costs. The guys I haven't been that bothered about I have let come to see me. I didn't realise it at the time, in fact it's only reading this post that I have noticed the difference.
Before I moved in with my partner, I would drive to see him every single day, and it is a half hour drive. I didn't mind at all. I had more free time and I knew he was working, so I would meet him at his after work. Now we live together and it's perfect. Honestly, if you love someone you'll make the effort to see them - so I would be questioning how your girlfriend really feels, if I was you.